1. Field of the Invention
This invention relates generally to turbojet aircraft engines and particularly relates to a lightweight, space-efficient actuation system for varying the divergent flap exit area of a gas turbine engine nozzle.
2. Description of Prior Developments
Current jet aircraft engine performance requirements dictate that the divergent flap exit area of two-dimensional convergent-divergent (2DCD) exhaust nozzles be controlled independently of the nozzle throat area to allow corresponding nozzle area ratios to be independently adjusted for all nozzle pressure ratios. Thrust vectoring can be obtained with these nozzles, if desired, by operating the upper and lower divergent flaps independently.
A conventional approach to actuating 2DCD nozzle divergent flaps, such as divergent flaps 10 shown in FIG. 1, requires the mounting of linear actuators 12 on nozzle side walls 14. This arrangement further requires bellcranks 15 and torque tubes 16 provided with arms 18 to transmit the actuation force to the divergent flaps 10. Due to the large range of motion through which the divergent flaps 10 must travel, extremely long linear actuators are required. The long length of these actuators makes it difficult to package them within the exhaust nozzle without cutting through structural bulkheads 20 and other nozzle actuation linkages.
As further seen in FIG. 1, tracks 22 and sliders 24 are required for preventing rotation of the linear actuators 12. Rotation of the linear actuators is prevented in order to reduce the size of the bulkhead holes required for accommodating the linear actuators and for preventing flexure of the hydraulic lines coupled to the linear actuators. This external actuation hardware, i.e. the tracks 22, sliders 24 and linear actuators 12 makes packaging of other actuation hardware difficult, if not impossible.
Another prior approach uses rotary actuators instead of linear actuators and their associated linkages. Such a system is shown in FIG. 2. Hydraulic motors (not shown) located within torque tubes 16 transmit power through a planetary gear drive to provide driving torque to the torque tubes. Several actuation arms 18 are located between the outer flap 25 and divergent flap 10. Arms 18 are provided with rollers 26 to transmit the driving torque to the divergent flaps 10.
This approach solves the external hardware packaging problem noted previously, but was found to be extremely heavy due to the weight penalty inherent with gears. This weight problem presents a significant drawback in aircraft applications where weight reduction is critical. Moreover, rotary actuators are expensive and not as reliable as linear actuators due to their inherent complexity.
Accordingly, a need exists for a light weight, cost effective, space efficient, and reliable divergent flap actuation system which minimizes the loads applied to the forward hinges which secure the divergent flaps within the engine nozzle.